Hot melt adhesives are applied to a substrate when molten, then placed in contact with a second substrate at which point the adhesive is cooled to harden the adhesive layer and form a bond. Hot melts are widely used for industrial adhesion applications, and are extensively used in product assembly and in packaging applications such as case sealing and carton closing operations.
Commercially available adhesives have until recently been applied at temperatures of 350° F. (177° C.) or greater in order to ensure complete melting of all the components and to achieve a satisfactory application viscosity. The need for such elevated temperatures increases operator risks with respect both to burns and to inhalation of residual volatiles and requires more energy, placing greater demands on the manufacturing facility.
Recent developments have led to hot melt adhesives that can be applied at lower temperatures, i.e., lower than 300° F. and down to about 200° F. One drawback, however, of low application temperature hot melt adhesives is their short open time, which makes their use impractical for packaging operations requiring hot melt adhesives with long open times to accommodate slower sealing applications.
There continues to be a need for improved hot melt adhesives, including adhesives having extended open times. The current invention fulfills this need.